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Hello, team.

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In this lesson, I'd like to talk with you about regular expressions.

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What is regular expression?

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Regular expression is a sequence of characters that define a search pattern.

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So you can use special set of characters to find all strings that match your pattern.

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Sometimes you use regular expression to split string.

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Let's imagine next case.

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You have a lot of text and you need to find only Google email accounts.

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How you would do this?

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You will try to describe search pattern with the help of special symbols.

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What are the special symbols?

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Here are some of them.

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Square brackets to identify characters which we need to search.

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I specified range from A to z lowercase and from A to z capital.

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Also specified dash character backslash d will match with all digits.

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And you already learned that we need to escape backslash character.

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That's why it's double backslash here.

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Also there are quantifiers.

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Plus sign might be read like this.

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In case these characters will be repeated at least one time and more.

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That is what we need after all of this.

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We expect at sign gmail dot.

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Taking into account dot in regular expression means any character we need to escape dot to say that

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we don't expect any character, but we are looking for exactly dot.

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That's why double backslash here and comb.

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Your homework task will be to learn other special symbols.

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I will share with you details at the end of the lesson.

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Definitely, there are a lot of ways to improve the regular expressions for email, and you can find

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in internet billions of variations of pattern for email address verification.

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Our goal right now to learn how to use regular expressions regarding special symbols to use in regular

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expression.

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I will share more details at the end of this lesson.

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After that you need to compile pattern.

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Do not forget to import Java.util regex package.

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We have the sample text with gmail address in it.

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Now you can get matcher much object out of pattern call matching method on pattern object and pass sample

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text into it.

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Match object can find matches call find method.

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Find method returns true in case a subsequence of the input sequence matches this matches pattern and

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false otherwise.

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In case there is a match, you will be able to call group method to return the string which matches

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your pattern.

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And let's print this to console.

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What can be improved here?

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As you learn loops, topic and control statements topic, you will be able to manage search process

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in a bit different way.

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For example, probably better solution would be here to call find method in if statement or in while

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loop to print multiple matches.

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But don't worry so far we will learn all topics gradually.

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You will have enough tasks to practice your skills.

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For now, I don't want to confuse you even more.

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Solution like this should be fine in case you want to find match in the string.

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Another example.

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We have sample text and we want to split it by sentences.

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Let's come up with a regular expression.

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We need to split by any of these characters.

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Period.

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Exclamation mark.

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Question mark.

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Now let's split this sample text.

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Using this regex we'll call split method.

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We'll get string array and let's print it to console.

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Here you can see that you have three different sentences.

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Let's recap what you have learned about strings.

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Now you know main string methods how to compare strings.

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You learn what is pool of strings.

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How to use escape sequences in your source code, how you can format strings, and how to use regular

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expressions.

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Now let's take a look at your homework.

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First of all, take a look one more time to string source code.

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Take a look at other methods which are in string class.

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As usual, I recommend you to read books.

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Chapter about strings.

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Learn format specifiers and flags.

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Here is the link to official Oracle documentation.

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I also did screenshots and left them here so you could faster find the things you need to learn.

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Do not forget to look through the examples of string formatting.

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Link to the source code is here.

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Implement console program according to requirements.

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This task to check your knowledge about string formatting.

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To learn regular expressions, I recommend you to use this resource.

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Let's take a look.

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You have 15 lessons.

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In each lesson you have description and exercise.

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You can always find hints on the right here.

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And in case you can't solve task.

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Take a look at solution here.

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Looking through the solutions will be also very efficient and will help you to learn regular expressions.

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I wouldn't say that you need to spend hours on learning regular expressions because you will not use

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them literally every day.

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But still, I would recommend you to learn the basics.

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And after that you have one more coding exercise to practice your skills in regular expressions.

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That's all for today.

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See you in the next lesson.

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Your.